This invention relates generally to coherent jet technology.
A recent significant advancement in the field of gas lancing is the development of the coherent jet technology disclosed, for example, in U.S. Pat. No. 5,814,125xe2x80x94Anderson et al. and in U.S. Pat. No. 6,171,544xe2x80x94Anderson et al. In the practice of this technology one or more high velocity gas jets ejected from one or more nozzles on a lance are maintained coherent over a relatively long distance by the use of a flame envelope around and along the high velocity gas jet(s). The flame envelope is formed by combusting fuel and oxidant ejected from the lance respectively from two rings of ports, an inner ring and an outer ring, around the high velocity gas jet nozzle(s). Typically the fuel for the flame envelope is ejected from the inner ring of ports and the oxidant for the flame envelope is ejected from the outer ring of ports. An extension on the lance perimeter forms a protected recirculation zone into which the high velocity gas jet(s) and the flame envelope fluids are provided from the nozzle(s) and ports. This recirculation zone enables some recirculation of the ejected fluids enabling improved ignition and improved stability of the flame envelope, thus enhancing the coherency and thus the length of the high velocity gas jet(s). The coherent jet(s) can be used to deliver gas into a liquid, such as molten metal, from a relatively long distance above the surface of the liquid. One very important application of this coherent jet technology is for providing oxygen for use in steelmaking operations such as electric arc furnaces and basic oxygen furnaces.
The recirculation extension, though constituting an improvement over earlier coherent jet systems, introduces certain problems concerning lance design and lance lifetime due to the need to water-cool the tip. These problems are of particular concern when the coherent jet system is used in a very harsh environment such as a basic oxygen furnace.
Accordingly, it is an object of this invention to provide a system which can produce effective coherent gas jets without the need for a lance extension or other element to establish a recirculation zone for the gases ejected from the lance.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for establishing at least one coherent gas jet comprising:
(A) passing at least one gas jet out from at least one nozzle housed in a lance having a lance face, said lance face having a ring of ports around the said at least one nozzle;
(B) passing fuel out from a first set of ports of said ring and passing oxidant out from a second set of ports of said ring; and
(C) combusting the fuel and the oxidant passed out from the first and second sets of ports of said ring to produce a flame envelope around the said at least one gas jet.
Another aspect of the invention is:
A coherent jet lance comprising:
(A) a lance having a lance face and having at least one nozzle having an opening at the lance face;
(B) a ring of ports on the lance face around the nozzle opening(s); and
(C) means for providing fuel to a first set of ports of said ring and means for providing oxidant to a second set of ports of said ring.
As used herein the term xe2x80x9clance facexe2x80x9d means the surface of a lance abutting an injection volume.
As used herein the term xe2x80x9ccoherent jetxe2x80x9d means a gas jet which is formed by ejecting gas from a nozzle and which has a velocity and momentum profile along a length of at least 20d, where d is the exit diameter of the nozzle, which is similar to its velocity and momentum profile upon ejection from the nozzle. Another way of describing a coherent jet is a gas jet which has little or no change in its diameter for a distance of at least 20d. 
As used herein the term xe2x80x9clengthxe2x80x9d when referring to a coherent gas jet means the distance from the nozzle from which the gas is ejected to the intended impact point of the coherent gas jet or to where the gas jet ceases to be coherent.